Ventricular Tachycardia (VT) is an arrhythmia characterized by an abnormally high rate of ventricular contraction. During VT the ventricles do not fill with sufficient amounts of blood prior to each contraction, often resulting in dizziness, loss of consciousness or sudden cardiac arrest. Catheter ablation has been shown to be an effective means for curing many arrhythmias, but current approaches are not able to coagulate tissue in the midmyocardium or subepicardial regions where foci responsible for VT often originate. In this phase I study we propose to develop and test a novel cooled-tip laser ablation catheter for coagulation of myocardium responsible for the initiation of VT. The novel design includes a proprietary fiber optic delivery system enclosed in a cooled tip that will allow diffusion of thermal energy into deeper layers of the myocardium while preventing damage to the endocardial surface. Additional features will allow real- time monitoring of the electrical activity at the arrhythmogenic site during treatment with the laser. Finally, an inexpensive low-powered diode laser used as the source should make the treatment a more practical clinical option. Experiments are planned to allow optimization of the catheter's delivery parameters in vitro followed by in vivo testing in canine hearts. We will assess the performance of the catheter in terms of lesion size (width, depth, and volume), lesion morphology, protection of the endocardial and epicardial surfaces, and proarrhythmic potential of healed lesions. Based on successful development of the catheter, phase II studies will be proposed to develop a more refined prototype with enhanced mapping capabilities and improved maneuverability. The device will subsequently be tested in a canine model of familial VT. PROPOSED COMMERCIAL APPLICATIONS: This research is specifically targeted towards the development of an improved laser-based catheter for treatment of VT. Cardiac arrhythmias including ventricular tachycardia (VT) and ventricular fibrillation (VF) are responsible for 400,000 cases of sudden death in the U.S. each year. Unlike other therapies, our catheter has potential for providing a curative means for patients who suffer from VT, and therefore could become the treatment of choice in such patients.